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Data Communication and Media
• Concept and Model of Communications• Analogy Signal and Digital Signal• Signal Frequency, Spectrum and Bandwidth• System Frequency Response and Bandwidth• Transmission Media and Types• Transmission Modes
- Parallel & Serial Transmission- Asynchronous & Synchronous Transmissions- Simplex & Duplex Transmission
• Communication Standards: RS/EIA-232 & Others
Lecture 1
General Communications: face-to-face conversation, write a letter, etc.
Electronic Communications: telephone, wireless phone, TV, radar, etc.
Lecture 1
Concept and Model of Communications
Our Focus Computer Communication
General Communication Model
Source TransmitterTransmission
SystemReceiver Destination
S(t) T(t) Tr(t) Sd(t)
MicrophoneTelephoneComputerScanner
TransformerEncoderCompressModulator
Line/CableFiber/AirSatelliteNetwork
TransformerDecoderUncompressDemodulator
SpeakerEarphoneComputerPrinter
Basic Communication Criteria: Speed, Reliability, Security (SRS)
Information must be converted into electrical energy, called signal, before transmission.
Text, voiceVideo, etc
Lecture 1
Analogy Signal and Digital Signal
Text, voiceVideo, etc
Digital
Analog
ConverterEncoder
t
t
s(t) voltage
s(t) voltage
Digital Signal
GeneralCommunication
Component – H()
Input Signal s(t) Output Signal o(t) =H[s(t)]
Digital-to-DigitalAnalogy-to-DigitalDigital-to-AnalogyAnalogy-to-Analogy
Analogy Signal
Signal Power: s (t)Signal Energy:
ʃ
2
s (t)dt2
4 classes/typesof systems- Input-to-Output
Signal
デジタル信号
Lecture 1
Signal Frequency, Spectrum and Bandwidth
Signal in time domainWave
Signal in frequency domainSpectrum
cos2πf1t
t
s(t)
Tperiod
Transformation
T=1/f1
f
S(f)
f1
s(t)=Acos2πf1t + Bcos2πf2t T=LCM(1/f1, 1/f2) f
S(f)
f1
A
f2
B
f: frequency
t
s(t)
Analogy Signal
t
s(t)
Digital Signal
S(f)=ʃs(t)e df-j2πf
Fourier Transformf
S(f)
f
S(f)
B = F2 – F1
Bandwidth
Bandwidth
Periodic
Aperiodic
F2F1
• Earthquake wave: 0.01 ~ 10 Hz
• Nuclear explosion signal: 0.01 ~ 10 Hz
• Electrocardiogram (ECG): 0 ~ 100 Hz
• Wind noise: 100 ~ 1000 Hz
• Speech: 100 ~ 4000 Hz (4 KHz)
• Audio: 20 ~ 20000 Hz (20 KHz)
• NTSC TV: 6 MHz
• HDTV: > 10 MHz
Lecture 1
Time-Frequency Relation and Signal Bandwidth
General Relations: Time Domain Frequency Domain Signal Bandwidth
Change Slow Low Frequency small
Change Fast High Frequency large
Frequency Unit: Hertz (Hz), Kilohertz (KHz), Megahertz (MHz), Gigahertz (GHz), Terahertz (THz)
Lecture 1
System Frequency Response & Bandwidth
System: H()Input Signal x(t) Output Signal y(t) =H[x(t)]
Input Spectrum: X(f) Output Spectrum: Y(f)
System Frequency Response: H(f) = Y(f)/X(f)
f
H(f)
System BandwidthB = F2 – F1
Signal can pass
Signal can’t pass
F1 F2
TransmissionBandwidth
Lecture 1
Transmission Media
A transmission medium: - a connection between a sender and a receiver- a signal can pass but with attenuation/distortion- a special system with a transmission bandwidth
Guided (Wired) Media(lines)
- Twisted pair (0~10MHz)- Coaxial cable (100K~500MHz)- Optical fiber (180~370THz)
Unguided (Wireless) Media(air, vacuum, water, etc.)
- LF (30~300KHz, Navigation)- MF/HF (300~3000KHz, AM/SW radio)- VHF (30~300MHz, TV & FM radio)- UHF (0.3~3GHz, TV, mobile phone)- SHF (3~30GHz, satellite, microwave)- EHF (30~300GHz, experimental com)- Infrared (no frequency allocation)
Transmission Media
Frequency and Spectrum
Propagation characteristics are different in each frequency band
LF HF VHF UHF SHF EHFMF
UV
1 MHz1 kHz 1 GHz 1 THz 1 PHz 1 EHz
infrared visible
X raysGamma rays
902 – 928 Mhz
2.4 – 2.4835 Ghz
5.725 – 5.785 Ghz
ISM band
30kHz 300kHz 3MHz 30MHz 300MHz 30GHz 300GHz
10km 1km 100m 10m 1m 10cm 1cm 100mm
3GHz
Lecture 1
Lecture 1
Parallel Transmission and Serial Transmission
Sender Receiver
…011000110111010111…?
Sender Receiver
0110001
7 (N) bits are sent together7 (N) lines are needed
Parallel Transmission
Sender Receiver
0 1 1 0 0 0 1
7 (N) bits are sent one after anotherOnly 1 line is needed
Serial Transmission
0110001
0110001
P/S converter S/P converter
… 01…00 01…10 11…10 10…11 …
N N N N
Segment the 0/1 stream into N bits groups
Timing or synchronization between a sender and a receiver is very important for data transmission
Lecture 1
Asynchronous and Synchronous Transmission
Asynchronous transmission:
1) A bit stream is segmented into small groups characters (5~8 bits)
2) Add a start bit (0) and a stop bit (1) at the beginning and end of each character
3) Frame = start_bit + character + stop_bit (7~10 bits), but 2/9~2/10 no real data
4) Arbitrary long gap/interval/idle between two characters or frames
Sender Receiver0110001 01 1001100 01 0011101 01
Synchronous transmission:
1) A bit stream is segmented into relative large groups/blocks many characters or bytes
2) Add control bits at the beginning and end of each block
3) Frame = H_control_bits + characters (data_bits) + T_control_bits
4) No gap/interval/idle between two characters in a data block/frame
Sender Receiver0110001Con_bits 1001100 0011101 Con_bits
1011100 01
1011100. . .
0110001
Independent clocks
Synchronized clocks
Frame4 Frame3 Frame1Frame2
Frame
idle
HeaderTrailer
Lecture 1
Simplex Transmission and Duplex Transmission
Device A Device BSimplexTransmission
Direction of data
Device A Device BHalf DuplexTransmission
Direction of data at time 1
Device A Device BFull DuplexTransmission
Direction of data all the time
Direction of data at time 2
One can send and the other can receive
Both can send and receive but in different time
Both can send and receive simultaneously
複信 - Wikipedia
Lecture 1
Communication Standards and Related Organizations
Communications need standards for inter-operations of different devices
Standard Organizations:- ISO (International Standards Organization): ISO number- ITU (International Telecommunication Union): V.num & X.num- EIA (Electronic Industries Association): EIA-num- IEEE (Institute of Electronics Engineers): IEEE.num- ANSI (American National Standards Institute): ASCII, etc.- ATM Forum and ATM Consortium- IETF (Internet Society and Internet Engineering Task Force): RFC num- W3C (World Wide Web Consortium): HTTP, HTML, XML, …- WAP Forum (Wireless Application Protocol): WAP-num
Lecture 1
Serial & Asynchronous Transmission Standards
Standards of transmission in short distance:- EIA-232 or RS-232- V.24- ISO 2110- EIA-449/RS-422/RS-423- EIA-530- X.21
Their common features- Serial & asynchronous transmission- Transmissions of ASCII code, byte, char- Use twisted copper lines - Low speed: several Kbits ~ Mbits per second- Short distance: < several tens of meters
Lecture 1
EIA/RS-232 Standard
Device ASender
Device BReceiver
• Transmit characters (7 or 8 bits)• Sender: 0 +15v and 1 -15v • Start bit (0) and stop bit (1) for every character 9/10 bits in total
• A sender never leaves wire at 0v; when idle, puts –15v, i.e., 1• Receiver: 0 (+3v, +15v) and 1 (-3v, -15v), otherwise error
Wave form of ‘+’, 2B or 0101101bit 0
RS-232, Wikipedia
Lecture 1
EIA/RS-232 Standard (cont.)
• Agreement of transmission timing or rate/speed bps bits per second, bit rate or transmission speed- 300bps, 2.4Kbps, 4.8Kbps, …, 19.2Kbps, 33.6Kbps, 56Kbps
• Setting bit rate (transmission speed) of devices/hardware- switch (manually), software, auto-detection
• Either simplex or duplex
T: Transmitter R: Receiver G: Ground
Lecture 1
EIA/RS-232 and Other Standards
• EIA-232: rate<64Kbps; connection length< 15 meters; 25 pin connector- pin 2: receive (RxD); pin 3: transmit (TxD); pin 7: groud- other pins for transmission control
• EIA-449: rate<10Mbps; connection length< 12 meters; 37/9 pin connector• EIA-530: same as the above; 25 pin connector• X.21: 64/192 Kbps (N-ISDN rate); 15/8 pin connector RS-232 - ウィキペディア
t
s(t)
Exercise 1
1. Two signals are given in the following figures. Whose bandwidth is large? Why?
t
s(t)
(a) (b)
2. Draw the RS-232 waveform diagrams of ASCII letters of R (1010010) and S (1110011).
3. Give at least one example for each of the following transmission/communication modes:parallel transmission, serial transmission, simplex transmission and duplex transmission.
4. Suppose one sent 10000 7bit characters across an EIA-232 or RS-232 connection that operated at 9600 bps (9.6Kbps). How long will the minimum transmission time be required? (Hint: remember to add a start bit and a stop bit on each character.)